Despite virologic suppression on ART, the levels of cellular immune activation and systemic inflammation rarely return to levels seen in HIV-1-seronegative individuals. We believe that a defect in extracellular adenosine (ADO) production in HIV-1+ individuals plays an important role in the inability of the ADO-A2AR- cAMP signaling pathway to suppress chronic HIV-1-associated inflammation. Extracellular ADO is generated in conditions of stress through hydrolysis of ATP by the ectoenzymes, CD39 and CD73. While these enzymes are co-expressed in murine regulatory T cells, in humans we have confirmed previous studies that they belong in separate CD4+ T cell subsets. Furthermore, we have observed decreases in the frequency and absolute numbers of CD4+CD73+ T cells in HIV-1 infection, regardless of virologic suppression on ART. CD4+CD73+ T cells inversely correlate with T cell immune activation as well as plasma levels of C-reactive protein (CRP). We hypothesize that decreased ADO production, due to the loss of CD4+CD73+ T cells, contributes to the inability of the ADO-signaling pathway to control the chronic inflammation in HIV-1 infection. We propose to conduct a phase I/II, randomized, double blind, placebo controlled, partial crossover pilot study evaluating the effect of Dipyridamole (DP), an FDA-approved drug proven to increase extracellular ADO levels, on cellular immune activation and inflammation. We will randomize 40 HIV-1+ subjects virally suppressed on ART and with CD4+ T cell counts d500 cells/mm3, to 12 weeks of either DP or placebo. The primary endpoints are the changes in the proportion of CD8+ T cell co-expressing CD38 and HLA-DR and the plasma levels of IL-6. Secondary endpoints will assess the impact of 12 and 24 weeks DP therapy on immunologic and virologic parameters including: CD4+ T cell activation and cell cycling, frequencies of T cell maturation subsets, monocyte and macrophage activation, gut mucosal T cell activation, plasma levels of biomarkers of inflammation and coagulation, and residual viral expression. In Aim 2, we will determine whether changes in the various immunologic parameters will translate to a measurable clinical outcome. As such we will evaluate whether DP therapy can improve vascular function by performing brachial artery flow-mediated dilation on the HIV-1+ subjects in our clinical trial. In Aim 3, since we have shown in vitro that ADO can suppress T cell activation and secretion of pro-inflammatory cytokines, we will investigate in vivo whether CD73 expression and the ADO-A2AR-cAMP signaling pathway can indeed regulate HIV-1-associated inflammation. We will determine frequencies of immune cells expressing CD73 in peripheral blood and gut mucosal tissue as well as the levels of the purines involved in the signaling pathway and investigate their associations with immune activation and inflammation. By elucidating specific mechanisms responsible for HIV-1-associated immune dysregulation, results of our study may lead to new interventions aimed at preventing or limiting the impact of chronic inflammation and immune activation in HIV-1 infection.